Reversible and Broad-Range Oxygen Sensing Based on\nPurely Organic Long-Lived Photoemitters

Abstract

The detection of\noxygen (O₂) by optical sensors is of\ngrowing importance, for example, in biology, life science, environmental\nscience, and aerodynamics, where the composition of gases is crucial\nfor many applications. Purely organic optical O₂ sensors\nare very attractive for monitoring food deterioration, biosensing,\nand biomonitoring, as they can provide continuous, reversible, and\nnondestructive O₂ sensing. However, purely organic optical\nreversible O₂ sensors that can work with a broad O₂ concentration range and that have robust reversibility are\nyet to be realized. We hereby developed a purely organic optical O₂ sensor by embedding polyimide-based photoemitters within\na poly­(vinyl alcohol) (PVA) matrix. The photoemitters are synthesized\nthrough one-pot hydrothermal reactions. They have a lifetime of room\ntemperature phosphorescence (RTP) of up to a few microseconds (μs)\nwhen they are embedded into the polymer matrix. Our results demonstrate\nthat the photoemitters have higher sensitivity and broader sensing\nrange to O₂ if they are synthesized with longer reaction\ntimes because they possess a more rigid polyimide structure. The O₂ sensor with such optimized photoemitters embedded in the\npolymer matrix exhibits continuous and broad-range O₂ sensing\nin the range of 0–16% O₂. The Stern–Volmer\nquenching constant (<i>K</i>_sv) was calculated\nto be 0.2351 kPa^–1 for the linear response range\nof 0–4% O_2. Moreover, the O₂ sensor can\nbe repetitively used at least 10 times in the linear range (0–4%\nO₂) or beyond the linear range (up to 21% O₂). The metal-free, purely organic sensors that enable the continuous\nand repetitive detection of O₂ within a relevant O₂ sensing range are appealing especially for monitoring packaged\nfood, biomonitoring, and biosensing.